Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. All heads that can read may be referred to as read heads herein, even if the head is also capable of other functions (e.g. writing) and/or includes other structures, such as a heater, laser, microactutor, lapping guide, etc.
In a modern magnetic hard disk drive device, each head is a sub-component of a head-gimbal assembly (HGA) that typically includes a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head-stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit (FPC). The plurality of HGAs are attached to various arms of the actuator.
Modern laminated flexures typically include flexure conductive traces that are isolated from a flexure structural layer by a flexure dielectric layer. So that the signals from/to the head can reach the FPC on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along a corresponding actuator arm and ultimately attaches to the FPC adjacent the actuator body. That is, the flexure includes flexure traces that extend from adjacent the head and continue along the flexure tail to a flexure tail terminal region that includes electrically conductive flexure bond pads adjacent the FPC.
The FPC includes electrically conductive FPC bond pads that correspond to the flexure bond pads of the flexure tail, and FPC conductive traces that lead from the FPC bond pads to a pre-amplifier chip. The FPC conductive traces are typically separated from a FPC stiffener by a FPC dielectric layer. The FPC may also include a FPC cover layer over the FPC conductive traces, the FPC cover layer having a window to allow electrical conduction to the pre-amplifier chip and access to the FPC bond pads. To facilitate electrical connection of the flexure bond pads to the FPC bond pads during the HSA manufacturing process, the flexure tails must first be properly aligned relative to the FPC. Then the flexure tails must be held or constrained against the FPC conductive electrical terminals while the aforementioned electrical connections are made (e.g. by ultrasonic bonding, solder jet bonding, solder bump reflow, or an anisotropic conductive film).
However, an undesirable electrical impedance discontinuity may exist at the location of where the flexure bond pads are electrically connected to the FPC bond pads. Such electrical impedance discontinuity may degrade the performance of the electrical trace connections to the read head. For example, the electrical impedance discontinuity may undesirably limit signal bandwidth and thereby limit maximum data transfer rate. Often it is not practical to attempt to reduce the impedance discontinuity by reducing the size of the flexure bond pads or the FPC bond pads in the design, because sufficient bond pad area is required during the bonding process to accommodate bond pad alignment uncertainty.
Accordingly, there is a need in the art for an improved FPC design that may reduce an electrical impedance discontinuity at the location of where the flexure bond pads are electrically connected to the FPC bond pads.